1. Field of the Invention
The present invention relates to enclosed area fire suppression methods and systems, and more particularly to enclosed area fire suppression methods adapted for use in settings which require high reliability yet minimal bulk, such as in aircraft.
2. Background Art
Enclosed area fire fighting methods are commonly used in aircraft and they may be used elsewhere as well. Critical features of these fire suppression methods are reliability and self-sufficiency. However, in aircraft and similar settings, efforts to minimize any on-board bulk, are also essential. This leads to long term efficiencies, including fuel savings Sometimes the bulkiest component in a fire fighting method is the extinguishant used to put out fire. As an example, this may be 300-400 pounds of Halon extinguishant in an aircraft system. Hence a difficult trade off sometimes arises between having an adequate system and one that saves bulk.
Minimum concentration of extinguishant within an enclosed area is necessary to suppress fire. A problem arises because the particular location of fire within a compartment is unpredictable. Thus, enclosed methods conventionally have filled a large sector entirely with a concentrated mixture of extinguishant. These methods do this essentially by thoroughly mixing extinguishant and air in the compartment.
Instead of selecting water as the extinguishant, aircraft fire suppression methods typically employ bromotrifluoromethane ("CBrF.sub.3 "), or a related compound bromochlorodifluoromethane, sold commercially as "Halon" compounds. Maintaining minimum concentration CBrF.sub.3 in a compartment for prolonged periods presents a special problem. CBrF.sub.3 is most practically stored onboard a vehicle or aircraft in liquid phase, under pressure. As pressure decreases during piping into the compartment, the CBrF.sub.3 vaporizes. Within a system having conduits, this phase change is transient, and therefore it is difficult to achieve a steady state flow. Consequently, during a lengthy dispersion there is substantial waste of CBrF.sub.3. U.S. Pat. No. 4,643,260--Miller addresses this problem. A pressure regulated conduit, formed by conduit sections 48, 52, and 56, which the patent shows, maintains the CBrF.sub.3 in the liquid phase to the point of discharge.
While the flow problem of CBrF.sub.3 has been addressed, the state of the art of enclosed area methods is still to try mixing extinguishants and air in the compartment. Because of the focus on mixing extinguishants with air, in many instances the thought of using the heavier-than-air characteristic of extinguishants is forgotten. CBrF.sub.3 in the gas phase is about five times denser than air; bromochlorodifluromethane is also substantially denser than air. Thus, CBrF.sub.3 descends through air, much as sand falls through water. The quantities of extinguishant which conventional methods use are unsatisfactorily large.
Another pertinent development has been improved techniques to detect fire quickly. For instance, fire detection methods in commercial aircraft detect fire in less than one minute. The implications of this capability include the fact that fire fighting methods which combat smaller, incipient fires have become more practical.
A search of the U.S. patent literature discloses the following:
U.S. Pat. No. 4,646,848 (Bruensicke) shows a fire suppression system for an aircraft having a main cabin, a plurality of subcompartments, and ducts 57 which connect the main cabin to the subcompartments. Once it is determined which subcompartment contains fire, a crew member with a hand held extinguisher directs an extinguishant through the appropriate duct to the fire.
U.S. Pat. No. 4,643,260 (Miller), the pressure controlled system for dispersing CBrF already discussed, discloses thorough mixing of extinguishant and air.
U.S. Pat. No. 3,524,506 (Weise) shows an apparatus which totally floods an aircraft compartment with an extinguishing agent.
U.S. Pat. No. 3,481,408 (Ward) shows a fire fighting aircraft which disperses a jet of extinguishant to put out a fire.
U.S. Pat. No. 2,452,348 (Beach) shows a discharge of extinguishing medium into an enclosure in such a way that the medium will sweep across the floor of the enclosure.
U.S. Pat. No. 2,292,794 (Paradise) shows a method where atomized moisture is dispersed above a fire and then allowed to descend on the fire. The moisture, which is sprayed from the ground to a location immediately above the fire, forms a bank or cloud over the fire. Then, heat from the fire vaporizes the moisture, expanding the cloud and extinguishing the fire.
U.S. Pat. No. 3,783,946 (Petrinec et al) shows a sequential extinguishant dispersion system, which maintains a concentration of extinguishant in an enclosed area for a prolonged period of time.